Next-to-leading-order (NLO) QCD corrections to \(A_t\)  have been computed in the limit of a large top quark mass [1]}, [2]}, [3]}, [4]}, [5]}
and later with the full mass dependence [6]}, [7]}, [8]}, [9]}, thus also providing NLO QCD corrections to \(A_b\) .
NNLO QCD corrections
in an expansion for a large top quark mass have been obtained in [10]}, [11]} and recently, exact numerical results became available [12]}.
Partial results in the limit of an
infinitely heavy top quark are known at next-to-next-to-next-to-leading order (N\(^3\) LO) [13]}.
NLO electroweak corrections, for which the above decomposition is not possible, have been obtained in [14]}, [15]}, [16]}, [17]}.
